The present invention relates to a process for removing volatile organic compounds (VOCs) from a latex using a membrane.
Latex paints often contain VOCs at levels that produce undesirable odors. These VOCs, typically ppm levels of low molecular weight ketones, alcohols, acetates, and aldehydes, are not essential for the paint's performance but are added to facilitate various steps in the paint's manufacture. Accordingly, paints free of these odor producing agents are desired.
Removal or “stripping” of trace amounts of low molecular weight organics can be accomplished by contacting a liquid containing VOCs with a gas, such as air, or nitrogen, or steam. The gas can be passed through a sparger to create large numbers of small bubbles dispersed within the liquid. The bubbles rise to the surface of the bulk liquid, carrying a portion of the VOCs with them. Other well-known methods for carrying out stripping operations involve contacting liquid and gas in a trayed or a packed stripping tower. In all of these devices, the organic compounds transfer from the liquid phase to the gas phase due to favorable liquid-vapor equilibrium partition ratios or relative volatilities.
Although these conventional stripping processes are widely used for treating aqueous streams, these techniques are not as efficient for removing VOCs from latexes. First, because latexes are stabilized by significant amounts of surfactant, sparging produces high volumes of foam during the stripping operation, thereby causing major problems in the processing and packaging of the finished latex. Second, there is a need for a more economical process that can increase interfacial area for mass transfer and thus reduce the size and cost of the stripping equipment. It would therefore be an advance in the art of VOC removal to find a way to reduce concentrations of VOCs in latex paints in a more efficient manner.